1. Field of the Invention
Exemplary embodiment of the invention relates to a liquid crystal display and a local dimming method thereof.
2. Discussion of the Related Art
A range of application for liquid crystal displays has gradually widened because of its excellent characteristics such as light weight, thin profile, and low power consumption. A backlit liquid crystal display controls an electric field applied to a liquid crystal layer and modulates light coming from a backlight unit, thereby displaying an image.
The image quality of the liquid crystal display depends on contrast characteristics. It is limited to an improvement of the contrast characteristics using only a method for controlling a data voltage applied to a liquid crystal layer of a liquid crystal display panel to modulate a light transmittance of the liquid crystal layer. Accordingly, a backlight dimming method for controlling a luminance of a backlight unit based on an input image is developed so as to improve the contrast characteristics, and thus greatly improves the contrast characteristics. The backlight dimming method adaptively controls the luminance of the backlight unit based on the input image to thereby reduce power consumption. The backlight dimming method includes a global dimming method for controlling a luminance of an entire display surface of the liquid crystal display panel and a local dimming method for locally controlling a luminance of a display surface of the liquid crystal display panel by dividing the display surface into a plurality of blocks.
The global dimming method may improve a dynamic contrast measured between two successively arranged frame periods. The local dimming method locally controls the luminance of the display surface during one frame period, thereby improving a static contrast that is difficult to improve using the global dimming method.
The local dimming method divides the backlight unit into the plurality of blocks to make a backlight luminance of a block corresponding to a bright image high, and to make a backlight luminance of a block corresponding to a relatively dark image low. Because the plurality of blocks each including light sources are individually turned on in the local dimming method, the backlight luminance in the local dimming method is less than a backlight luminance measured when all of the light sources of the backlight unit are turned on. To compensate for the low backlight luminance in the local dimming method, pixel data is multiplied by a predetermined gain, and thus can be compensated. In the local dimming method, when the pixel data is compensated, there occurs the grayscale band phenomenon, in which high gray levels look like the same brightness. Hence, the image quality degradation may be generated. For a reduction in the image quality degradation, a dimming curve for selecting a dimming value based on a representative value of each block may use a dimming curve, in which most of gray levels increase. In this case, an improvement effect of the image quality can be obtained. However, because the dimming values mapped to most of the representative values of the blocks increase, a reduction effect of the power consumption is not satisfactory.